The present invention relates to means for cooling and lubricating rotating objects in rotary machines, especially for high-speed applications, and more particularly to means for cooling and lubricating bearings for jet engines, turbines and the like.
Lubrication is important to rotary machines, particularly to bearings at high-speed applications. Ball bearings are popularly used in gas engines and turbines. In such applications, the ball bearings generally work at very high speeds under high load and have to meet the requirements of very demanding rotor dynamics. Obviously, the life of a bearing is directly related to the adequate lubrication and cooling of its wear surfaces. A ball bearing generally has a cage ring disposed between an outer ring and an inner ring. The cage ring includes pockets to locate individual balls in a circumferentially spaced relationship between an outer race and an inner race defined by the respective outer and inner rings. The cage ring is often radially restrained by the inner ring. Experience has shown that for such cage, a non-uniform cage ring support by the inner ring can occur. Due to higher temperatures of the loaded half of the inner ring, its land diameter guiding the cage, is larger and the cage is supported predominantly on the single land rather than on the two lands. A residual cage ring unbalance force together with the reaction applied to the cage by a single inner ring land generate cage ring tilting moment to produce impact loading between one or a number of the bearing balls and the pockets of the cage ring retaining these particular bearing balls. The impact loading will result in distress on and damage to the bearing balls and the pockets of the cage ring.
Efforts have been made to improve the lubricating system for high speed ball bearings. One example of the lubricating system is described in U.S. Pat. No. 3,980,359, issued to Wetherbee, Jr. on Sep. 14, 1976. Wetherbee, Jr. describes a lubricating system for high speed ball bearings. The ball bearing includes an outer ring, a split ring, a split inner ring having a fore ring and an aft ring, a cage and a plurality of spherical balls journalled therebetween. The lubricating system includes forming the cage into the scalloped ring and rotatably supporting it in an annular channel formed between the split inner ring halves. The lubricating system further includes machined passageways in the split face to communicate the channel and a V-shaped annular oil collecting groove in the most inner surface of the inner ring. The side walls of the scalloped ring and the channel are dimensioned to define a gap for leading oil to and from internally of the bearing.
Annuluses have been used in rotating objects of rotary machines, particularly in high speed applications, for collecting lubricant fluids and maintaining an amount of the lubricant fluids therein under centrifugal forces to ensure the lubricant fluids supply. U.S. Pat. No. 5,119,905, issued to Murray on Jun. 9, 1992 describes an accessory drive spline lubrication system for a turbine engine reduction gearbox. In order to prevent the continuing loss of engine oil resulting from an ineffective seal, the spline area of a drive shaft is provided with oil by an annular reservoir which collects oil shot from a nozzle. The oil under centrifugal forces is maintained in the annular reservoir and the oil axially enters the spline area when more oil is collected in the annular reservoir.
Nevertheless, further improvements for a simple and cost effective solution of the lubrication and cooling of high speed rotating objects in rotary machines, especially of high speed bearings, are still desired.
One object of the present invention is to provide a means for directing cooling and lubricant fluids under centrifugal forces in a rotary machine.
Another object of the present invention is to provide means to improve cooling and lubricating ball bearings with split inner rings.
A further object of the present invention is to provide improved ball bearings using only features designed at the vicinity of the inner ring split faces.
In accordance with one aspect of the present invention, a channel for collecting and directing cooling and lubricant fluids under centrifugal forces in a rotary machine is provided. The channel comprises an annular groove disposed in an annular inner surface of a rotating object of the rotary machine. The annular groove has in a cross-section, an open side towards a rotating axis of the rotating object, a first section radially distal from the open side and a second section disposed radially between the open side and the first section. The rotating object includes at least one radial passage extending therein to communicate with the annular groove and an area of the object to be lubricated. The at least one radial passage includes an aperture in the annular groove located in the second section such that the first section of the annular groove acts as a reservoir when cooling and lubricant fluids under the centrifugal forces are collected in the annular groove and then delivered through the at least one radial passage into the area.
In accordance with another aspect of the present invention, a ball bearing includes an outer ring defining an outer race; an inner ring defining an inner race. A plurality of balls are retained between the outer and inner rings. An annular groove is disposed on an innermost surface of the inner ring. The annular groove has in a cross-section, an open side, a first section disposed radially distal from the open side and a second section disposed radially between the open side and the first section. A plurality of radial passages extend through the inner ring from the annular groove to the inner race. Each of the radial passages has an aperture in the second section of the annular groove.
The cross-section of the annular groove is preferably non-rectangular.
In accordance with one embodiment of the present invention, a ball bearing includes an outer ring defining an outer race and an inner ring including a pair of juxtaposed first and second ring elements defining an inner race. The first and second ring elements have flat surfaces abutting each other, usually called split faces. A plurality of balls are retained between the outer and inner rings and circumferentially spaced apart from one another by a cage ring disposed between the outer ring and the inner ring. The cage ring is often piloted on outermost cylindrical surfaces of the inner ring elements, usually called cage lands. The diameter of the cage lands is slightly smaller than the inner diameter of the cage, such that there is a small annular gap between the cage ring and the inner ring cage lands. An annular groove is disposed on an innermost surface of the inner ring at abutting faces of the first and second ring elements. The annular groove has a non-rectangular cross-section with an open side towards a rotating axis of the bearing. The non-rectangular cross-section is defined by first and second sections in a radially disposed relationship and the second section includes the open side. On the abutting face of the first or second ring elements, a plurality of grooves radially extend therethrough to form radial passages between the inner race and the annular groove when the first and second ring elements are placed together. Each of the radial passages has an aperture in the annular groove located in the second section of the annular groove such that the first section of the annular groove acts as a reservoir when cooling and lubricant fluids under a centrifugal pumping force are collected in the annular groove and then delivered through the radial passages into the inner race.
With such a configuration, the lubricant fluids, preferably oil, fed into the inner race are circumferentially balanced by the annular reservoir, which will provide more efficient cooling and lubrication to the sliding points within the bearing. For the same purpose, the number of radial passages should not be too few and will depend on bearing size, speed and load. In a presented embodiment, 14 radial passages are provided. The annular groove advantageously provides not only a reservoir function but also additional cooling capability, especially if it is located at the bore of the loaded half of the inner ring. Such an arrangement allows minimization of temperature difference between loaded and non-loaded inner ring halves and provides uniform and stable support to the cage. Also, due to better oil distribution, the contact zone temperatures will be reduced significantly. Therefore, the better cooling and lubrication will improve bearing performance and the bearing life.
Other advantages and features of the present invention will be better understood with reference to a preferred embodiment described hereinafter.